The present invention relates to a self-propelled snowplow vehicle having a driving wheel for driving the snowplow vehicle and an auger for removing snow.
In a snowplow vehicle equipped with a snow-removing anger, a system is employed to ensure that the vertical level or height of the auger can be changed in view of snow-removing conditions. When the snowplow vehicle moves from one place to another, the auger is preferably kept in a raised position to facilitate smooth movement of the snowplow vehicle. On the other hand, when a snow-removing operation is to be achieved, the auger is preferably moved to a lower position to achieve the snow-removing operation with improved efficiency. During the snow-removing operation, the auger is frequently raised and lowered in harmony with angulations on the ground surface. Frequent rising and lowering operation of the auger, when achieved manually, is laborious. To lighten the load on the human operator, an improved self-propelled snowplow vehicle has been proposed, which is equipped with a power-operated vertically swingable auger, as disclosed in Japanese Patent Laid-open Publication No. HEI 4-194109.
The disclosed snowplow vehicle includes a propelling frame equipped with left and right crawler belts, a vehicle frame equipped with an auger and pivotally connected to the propelling frame, and a lift control device operable to lift a front end portion of the vehicle frame up and down relative to the propelling frame. The lift control device is comprised of a cylinder actuator operable, under the control of a control unit, to extend or contract its piston rod to thereby lift the vehicle frame front end portion and the auger in an upward or a downward direction in response to pivotal movement of a manual operating lever provided on an operating part of the snowplow vehicle.
The cylinder actuator constituting the lift control device needs a power source for operation thereof. In the case where the cylinder actuator is an oil hydraulic cylinder actuator, a separate hydraulic power unit must be provided. Accordingly, the overall size of the lift control device is relatively large. Thus, the use of the oil hydraulic cylinder actuator is quite disadvantageous when the snowplow vehicle is relatively small in size.
In order to achieve downsizing of the lift control device, use of an electro-hydraulic cylinder actuator may be considered. The electro-hydraulic cylinder actuator has an electric motor drivable to produce a hydraulic pressure used for reciprocating a piston rod of the cylinder actuator. The electric motor and a hydraulic power unit such as a pump are assembled with a cylinder of the cylinder actuator, so that the electro-hydraulic cylinder actuator is relatively small in size. The electric motor is controlled to extend or contract the piston rod of the cylinder actuator to thereby raise or lower the auger in response to on-off operation of an operation switch.
Since the height of the auger is changed in view of snow-removing conditions, it may occur that the operation switch is kept in the activated state even after the piston rod arrives at its fully extended or fully contracted position. On this occasion, the electric motor is subjected to a heavy load for a long time. Additionally, during snow-removing operation, since the height of the auger is frequently changed in harmony with angulations of the ground surface, the electro-hydraulic cylinder actuator is forced to operate repeatedly with high frequencies. Under such condition, the duty cycle of the electric motor is very high and generation of heat from the electric motor is promoted.
To deal with this problem, use of a continuously operable electric motor may be considered. The continuously operable electric motor is, however, expensive and hence increases the cost of the snowplow vehicle. As an alternative measure, use of a thermo-breaker may be considered for the purpose of protecting the motor from overheating. The thermo-breaker is generally built in the electric motor and operates to cut off or open a power supply circuit to the electric motor when the electric motor heats up above a given temperature.
The thermo-breaker is designed to continue the xe2x80x9copenxe2x80x9d state of the power supply circuit until the electric motor cools to a satisfactory operating temperature. Accordingly, a downtime occurs each time the thermo-breaker operates. In case where the operating temperature of the thermo-breaker is set to a relatively low value, the power supply circuit to the electric motor may be frequently cut off by the thermo-breaker. Alternatively, when the operating temperature of the thermo-breaker is set to a relatively high value, the power supply circuit to the electric motor may be cut off infrequently. In the latter case, however, the thermo-breaker requires a relatively long time to recover its original inoperating state. To enable smooth snow-removing operation, the frequency of operation of the thermo-breaker should preferably be reduced
To this end, an arrangement may be considered, in which a detection switch is associated with the electro-hydraulic cylinder actuator such that when arrival of the piston rod of the cylinder actuator at its fully extended or fully contracted position is detected by the detection switch, the detection switch generates a signal to stop operation of the electric motor. This arrangement may reduce the occurrence of overloaded condition of the electric motor. However, use of the detection switch necessarily increases the number of parts of the cylinder actuator and requires an electric wiring system, leading to an increased cost of the snowplow vehicle.
FIGS. 16A to 16C are diagrammatical views illustrative of the operation of a conventional self-propelled snowplow vehicle 500. In FIG. 16A, the snowplow vehicle 500 is shown with a snow-removing auger 503 disposed in a lowermost horizontal position. The snowplow vehicle 500 is moving forward by the action of crawlers 501 (one being shown) while removing snow by means of the auger 503 and a blower 504 rotatably driven by an engine 502. The auger 503 collects snow and the blower 504 blows the collected snow away from the snowplow vehicle 500 through a shooter 505. In this instance, a travel control lever 511 provided on a control board 510 is disposed in an xe2x80x9cFxe2x80x9d (forward) position, and an auger lift control lever 512 also provided on the control board 510 is disposed in a xe2x80x9cDNxe2x80x9d (down) position.
Due to a large amount of snow to be removed or in order to change the advancing direction of the snowplow vehicle 500, the snowplow vehicle 500 is occasionally moved backward. In this instance, as shown in FIG. 16B, the travel control lever 511 on the control board 510 is shifted from the xe2x80x9cFxe2x80x9d (forward) position to an xe2x80x9cNxe2x80x9d (neutral) position as indicated by the arrow {circle around (1)} whereupon the snowplow vehicle 500 stops moving in the forward direction. Then, the auger lift control lever 512 is shifted from the xe2x80x9cDNxe2x80x9d (down) position to an xe2x80x9cUPxe2x80x9d (up) position as indicated by the arrow {circle around (2)} whereupon lift cylinder actuators 506 (one being shown) operate to extend their piston rods to thereby lift a front end portion of a vehicle frame 508 upward relative to a propelling frame 507 on which the crawlers 501 (FIG. 16A) are mounted. The auger 503 is thus raised to an uppermost elevated inclined position.
Then as shown in FIG. 16C, the travel control lever 511 on the control board 510 is shifted from the xe2x80x9cNxe2x80x9d (neutral) position to an xe2x80x9cRxe2x80x9d (reverse) position as indicated by the arrow {circle around (3)} whereupon the snowplow vehicle 500 moves backward. As described above, in order to reverse the snowplow vehicle while moving in the forward direction, the conventional snowplow vehicle requires three consecutive steps of manual operation as indicated by the arrows {circle around (1)}-{circle around (3)}. Conversely, when the snowplow vehicle while moving backward is to be moved in the forward direction, the snowplow vehicle is first stopped from moving backward. Then, the auger is lowered from the uppermost inclined position to the lowermost horizontal position. Finally, the snowplow vehicle is moved in the forward direction. Thus, three consecutive steps of manual operation are also required. Due to complicated manual operations of the two levers 511, 512 to be done in a correct order, the maneuverability of the conventional snowplow vehicle is relatively low.
To deal with this problem, an improved snowplow vehicle has been proposed, wherein a snow-removing unit such as an auger is automatically raised when a reversing operation of the snowplow vehicle is selected, as disclosed in Japanese Utility Model Laid-open Publication No. SHO 64-28416. As shown in FIG. 17A, when a travel control lever 611 on a control board 610 is shifted to an xe2x80x9cFxe2x80x9d (forward) position, the snowplow vehicle 600 moves forward as indicated by the arrow while, at the same time, an auger 603 rotates to thereby achieve snow-removing operation. When the travel control lever 611 on the control board 610 is shifted to an xe2x80x9cRxe2x80x9d (reverse) position, as shown in FIG. 17B, the auger 603 is moved upward from the lowermost horizontal position of FIG. 17A through a neutral position (not shown) to an uppermost inclined position of FIG. 17B. Upon arrival of the auger 603 at the uppermost inclined position, rotation of the auger 603 is stopped by disengaging an auger clutch (not shown) disposed between the auger 603 and an engine (not designated). At the same time, the snowplow vehicle 600 is driven to move in the reverse direction as indicated by the arrow shown in FIG. 17B.
Since the auger 603 is lifted up to the uppermost inclined position each time the reverse position is selected by the travel control lever 611, this means that when the snowplow vehicle 600 is then to be moved forward to achieve a snow-removing operation, the auger 603 needs to be lifted down from the uppermost inclined position to the lowermost horizontal position. Due to a long downward stroke of the auger 603, an interruption occurs in the snow-removing operation each time the xe2x80x9cFxe2x80x9d (forward) position is selected immediately after the reversing mode of the snowplow vehicle. In other words, lifting of the auger 603 to the uppermost inclined position in preparation for the backward movement of the snowplow vehicle will lower the efficiency of the snow-removing operation. Due to this difficulty, the snowplow vehicle 500 shown in FIGS. 16A-16C is normally used notwithstanding the fact that the snowplow vehicle 500 is not satisfactory in terms of the maneuverability and lightening of load on the operator.
It is, accordingly, an object of the present invention to provide a self-propelled snowplow vehicle, which can be manufactured at a relatively low cost, is able to lighten the load on an electric motor of a electro-hydraulic cylinder actuator used to raise or lower a snow-removing member such as an auger, and is capable of achieving a snow-removing operation smoothly and efficiently.
According to the present invention, there is provided a self-propelled snowplow vehicle comprising: a propelling frame equipped with driving wheels for driving the snowplow vehicle; a vehicle frame equipped with an auger at a front end portion thereof for removing snow, the vehicle frame being pivotally connected to the propelling frame; a frame lift mechanism for lifting the front end portion of the vehicle frame up and down relative to the propelling frame, the frame lift mechanism including an electro-hydraulic cylinder actuator having a piston rod and an electric motor rotatably driven to produce a fluid pressure for reciprocating the piston rod between a fully contracted position and a fully extended position; an operation switch adapted to be manually activated to drive the electric motor in either direction; and a control unit for controlling operation of the electric motor thereby to control operation of the frame lift mechanism.
In one preferred form of the present invention, the control unit is arranged to forcibly stop the electric motor when a predetermined time has elapsed after the operation switch is activated, the predetermined time being equal to an operating time of the cylinder actuator which is required to extend or contract the piston rod over a maximum stroke defined between the fully extended position and fully contracted position.
By thus forcibly stopping the electric motor, it is possible to cut down the operating time of the electric motor. Since the electric motor is released from a heavily loaded condition soon after the arrival of the piston rod at its fully extended or contracted position, the load on the frame lift mechanism including the electric motor is lessened and the durability of the frame lift mechanism is increased.
Additionally, since the electric motor is stopped when the piston rod moves over the maximum stroke, generation of heat from the electric motor can be suppressed. The thermo-breaker built in the electric motor does not operate, so that the operator is allowed to continue snow-removing operation of the snowplow vehicle without considering a downtime of the snowplow vehicle which may occur when the thermo-breaker operates. The snow-removing operation can, therefore, be achieved smoothly and efficiently. Furthermore, the electro-hydraulic cylinder actuator (frame lift mechanism) can operate smoothly and reliably without requiring detection switches provided for detecting the piston rod arrived at the fully extended position and the fully contracted position. The snowplow vehicle is, therefore, formed by a reduced number of parts used and has a relatively simple electric wiring system. This achieves cost cutting of the snowplow vehicle.
It is preferable that the control unit continues to stop the electric motor when the operation switch is still in the activated state even after the lapse of the predetermined time.
When the operation switch is still in the activated state even after the electric motor is forcibly stopped upon the lapse of the preset reference time (which is equal to an operating time required for the electro-hydraulic cylinder actuator to move the piston rod over the maximum stroke), the control unit continues to stop the electric motor. Thus, a heavily loaded condition of the electric motor does not recur with the result that the total load exerted on the frame lift mechanism including the electric motor is reduced and the durability of the frame lift mechanism is increased. Additionally, since the thermo-breaker is kept in the off or inactivated state, a downtime does not occur. Thus, the snow-removing operation can be continued smoothly and efficiently.
In another preferred form of the present invention, the control unit is arranged to add up running times of the electric motor during which the electric motor is rotating and forcibly stop the electric motor when a total sum of the running times reaches a predetermined reference value. The predetermined reference value corresponds to a time which is required for the electric motor to heat up above a predetermined temperature. By forcibly stopping the electric motor, it is possible to protect the electric motor from overheating and eventually improve the durability of the electric motor. Additionally, the electric motor is stopped rapidly without operating the thermo-breaker built in the electric motor The control of the electric motor depends on time and does not rely on the thermo-breaker which requires a relatively long time for recover its original inoperating state. It is, therefore, possible to resume rotation of the electric motor in a relatively short period of time. Since snow-removing operation of the snowplow vehicle can be continued without considering a downtime which may occur when the thermo-breaker operates, the efficiency of the snow-removing operation is very high.
It is preferable that the total sum (Tm) of the running times is obtained by the expression
Tm=Trxe2x88x92Ts
where Tr represents an accumulated total of the running times during which the electric motor is rotating, and Ts represents an accumulated total of the rest times during which the electric motor is at a standstill.
It may be considered that the cumulative running time Tr is a total sum of the running times of the motor during which the electric motor heats up while it is rotating, and the cumulative rest time Ts is a total sum of the rest times of the motor during which the electric motor cools down while it is at a standstill. By using the integrated value or total sum Tm of rotating times which is represented by the expression Tm=Trxe2x88x92Ts, control of the electric motor is achieved in close match with actual heat-developing and -releasing conditions of the electric motor. Since the cumulative rest time (heat-releasing time) Ts of the electric motor is subtracted from the cumulative running time (heat-developing time) Tr, it is possible to elongate the time during which the integrated value or total sum Tm of running times reaches the preset reference value. This means that the time period during which the motor continues to rotate before it is forcibly stopped can be extended. The snow-removing operation of the snowplow vehicle can be achieved with improved efficiency.
It is further preferable that the control unit continues to stop the electric motor until a preset fixed time has passed after forcible stop of the electric motor. Since the heat developed in the electric motor is further released, the electric motor is protected from overheating with higher safeness and hence has a higher degree of durability.
Preferably, the running times of the electric motor have a fixed value and are added up at the lapse of a unit time, and the rest times of the electric motor have a fixed value and are added up at the lapse of the unit time, and wherein the fixed value of the running times is larger than the fixed value of the rest times.
In still another preferred form of the present invention, the snowplow vehicle has three modes of operation including a manual-up mode in which the auger is raised manually, a manual-down mode in which the auger is lowered manually, and an auto-up mode in which the auger is automatically raised, wherein the control unit is arranged such that when the manual-down mode is selected, the control unit determines and stores an amount of contraction of the piston rod achieved in the selected manual-down mode, and when the manual-down mode is followed by the auto-up mode and information representing reversing of the direction of rotation of the driving wheels is received, the control unit performs an auto-up control of the piston rod in which the piston rod is extended by an amount equal to the amount of contraction of the piston rod determined with respect to the preceding manual-down mode.
The travel condition of the snowplow vehicle, which may occur immediately before the manual-down mode is selected, is considered to be a road traveling condition in which the snowplow vehicle travels on a road surface with the auger held in an uppermost position, or a reversing condition in which the snowplow vehicle travels backwards on a snow-covered road surface with the auger held in an elevated position intermediate between the uppermost inclined position and a lowermost horizontal position. The auger, as it is in the elevated intermediate position, does not interfere with snow while the snowplow vehicle is moving backward. From this, it is preferable that when the auto-up mode is selected, the auger is raised to the elevated intermediate position. The auger is thus automatically returned to the previous position, so that there is no possibility of interference occurring between the auger and snow when the snowplow vehicle is moving backward. Furthermore, at the time of forward movement of the snowplow vehicle, the auger is lifted down from the elevated intermediate position to the lowermost horizontal position. Thus, the time required for lowering the auger is reduced to one-half of the conventional snowplow vehicle discussed above with reference to FIGS. 17A and 17B, so that the efficiency of the snow-removing operation is increased correspondingly. In addition, since the auger is automatically lifted to the elevated intermediate position, the operator is not subjected to undue load or pressure.
It is preferable that the piston rod of the electro-hydraulic cylinder actuator is extended and contracted at the same speed, and the amount of contraction of the piston rod is determined depending on time. This arrangement obviates the need for a stroke sensor provided for measuring the amount of extension or contraction of the piston rod, which sensor is expensive, is susceptible to malfunction due to adhesion of snow or dirt, and requires wire harnesses.
Preferably, the self-propelled snowplow vehicle further includes an auger clutch disposed between a power source and the auger for transmitting rotational power from the power source to the auger, wherein when the auger clutch is in an disengaged state, the control unit disables the auto-up control of the piston rod of the cylinder actuator.
The above and other objects, features and advantages of the present invention will become manifest to those versed in the art upon making reference to the following description and accompanying sheets of drawings in which certain preferred structural embodiments incorporating the principle of the invention are shown by way of illustrative examples.